The exemplary embodiment relates to image processing. It finds particular application in connection with the mapping of images from a higher to a lower dynamic range.
The “dynamic range” of a scene, image, or a reproduction device is defined as the ratio between the highest and lowest luminance levels. Recent technologies have made it relatively easy to create radiance maps for High Dynamic Range (HDR) sceneries. Conventional low dynamic range (LDR) reproduction devices, such as printers and CRT monitors, are typically 8-bit, i.e., the luminance can range in integer values from 0 to 255. These devices are not able to directly reproduce high dynamic range images (usually 12, 16, or even 32 bits per channel). However, realistic reproduction of high contrast scenery on conventional reproduction devices is required in the printing industry, photographing industry, and for computer graphics.
If the same quantization step is used to convert from high to low dynamic range, then either the brightest part of the image or the darkest part of the image is often lost. Several tone reproduction techniques for dynamic range compression have been proposed. However, most of these techniques are unable to reproduce the local contrast and fine details of the scenery and tend to introduce artifacts. Techniques that attempt to overcome this drawback are frequently computationally expensive. In addition, these methods generally include image-dependent manual parameter adjustments, which makes them hard to be utilized in an automated display or printing process.